1. Field of the Invention
The present invention relates to new organometallic complexes comprising elements belonging to the group of lanthanides, their preparation and their use in the stereospecific polymerization of unsaturated monomers.
A metal belonging to the group of lanthanides means, as generally accepted in the known art, a metal belonging to the group comprising: Scandium, having atomic number 21, Yttrium, having atomic number 39, and/or a metal having an atomic number of between that of Lanthanium (57) and Lutetium (71); these metals form part of group IIIA of the periodic table, according to the IUPAC definition prior to the year 1985.
2. Description of the Related Art
It is known in the art that the halides of lanthanides form a group of products used as precursors, both for the preparation of a large number of organometallic derivatives of lanthanides, and for the embodiment of particular catalytic processes, such as for example the polymerization of unsaturated monomers.
Their preparation is easy but their use is complicated by their complete insolubility in all hydrocarbons of any type, because they are characterized by polymeric-type structure, with halogen bridges and difficult to break.
A complete description of the crystalline and molecular structure of the halides of lanthanides can be found in the well-known treatise on structural inorganic chemistry edited by A. F. Wells "Structural Inorganic Chemistry" published by Clarendon Press, Oxford, 1975.
However, precisely because of this compact structure, when these halides are used as precursors in the synthesis of organometallic derivatives, it is necessary to resort to the use of basic-type reaction solvents, such as ethyl ether or tetrahydrofuran, which are capable of breaking their polymeric structure, making them more vulnerable to the chemical reagents with which they are to react.
This technique cannot be used however when the same halides are to be used in the preparation of catalytic systems, such as in the case of polymerization, in which the basic environment of the solvent is not compatible with the reagents in use and with the catalysis mechanism.
The known art describes an elegant method for breaking the above polymeric structure of lanthanide chlorides. This method consists in preparing complexes having the general formula: EQU Me(Ar)(AlCl.sub.4).sub.3
wherein: Me represents a metal belonging to the group of lanthanides and Ar represents a substituted or non-substituted benzene group.
Valid preparative methods for derivatives wherein Me is lanthanium, neodymium, samarium and X is chlorine, are disclosed in articles appearing in the magazines: a) Organometallics, vol. 4, page 942 of 1985 and vol. 6 page 1275 of 1987; b) Journal of Organometallic Chemistry, vol. 376, page 51 of 1989 and vol. 377, page 61 of 1989.
The crystalline and molecular structure of the complexes indicated in the above articles, show the presence of monomeric units MeCl.sub.3 complexed with 3 AlCl.sub.3 groups and an aromatic hydrocarbon binder.
In spite of the fact that the complexes of the known art having the general formula Me(Ar)(AlCl.sub.4).sub.3 quoted above, contain, as can be seen, the MeCl.sub.3 groups in monomeric form, they still have the great disadvantage however of being completely insoluble in aliphatic hydrocarbons.
This characteristics considerably limits their use in all reactions, such as for example the polymerization of olefins and diolefins, in which the solubility of the catalyst precursor is greatly desired for its simplicity of use and reproducibility of the catalytic activity.